Download/Embed scientific diagram | Geological map of Cambay Basin, western India. from publication: Early Eocene equatorial vegetation and depositional. In the southern Cambay Basin, it was sourced from a higher plant fraction deposited in marine or fluvial deltaic environment (Sivan et al., ). It is based on the Sub-surface study of on oil field in Cambay basin. After a brief description of the Cambay basin’s geology, the other aspects of exploration were .
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The NW-SE Dharwarian tectonic trends got rejuvenated creating a narrow rift graben extending from the Arabian sea south of Hazira to beyond Tharad in the north.
The Middle Eocene witnessed a regressive phase with oscillating conditions of deposition and development of deltaic sequences in the entire basin. Cammbay, the rift valley expanded with time. During Early Eocenea cammbay and widespread transgression resulted in the deposition of a thick, dark grey, fissile pyritiferous shale sequence, known as the Cambay Shale.
The end of the Paleogene witnessed a major tectonic activity in the basin resulting in the development of a widespread unconformity. The end of deposition of geolofy Olpad Formation is marked by a prominent unconformity. More than exploratory wells have been drilled in Cambay Basin.
Reservoir Rock There are a number of the reservoirs within the trapwacke sequence geolohy the Olpad Formation. From north to south, the blocks are:. The magnetic anomaly map also depicts the broad structural configuration of the basin. During Paleocenethe basin continued to remain as a shallow depression, receiving deposition of fanglomerate, trap conglomerate, trapwacke and claystone facies, especially, at the basin margin under a fluvio—swampy regime.
These consist of sand size basalt fragments. The Bouguer anomaly map has helped in identification of the major structural highs and lows in the basin. The same is true for the Basib Shale. In the northern part of the Ahmedabad-Mehsana Block, coal, which is well developed within the deltaic sequence in Kalol, Sobhasan and Mehsana fields, is also inferred to be an important hydrocarbon source rock.
Different Tectonic Zones with in the Basin The Cambay rift valley is bounded by well demarcated basin margin step faults. The associated unconformity also helped in the development of secondary porosity. Similarly, the Proto—Narmada river system was active in the south, supplying sediments from provenance, lying to the east.
These sediments are characterised by an assortment of illsorted, high energy trap derived materials.
Shales within the Miocene section in the Broach depression might have also acted as source rocks. A total of more than 30, LKM of conventional data has been acquired. This shale sequence has been divided into Older and Younger Cambay Shale with an unconformity in between.
Pliocene was a period of both low and high strands of the sea level, allowing the deposition of sand and shale.
The end of Cambay Shale deposition is again marked by the development of a basun unconformity that is present throughout the basin.
Oligocene — Lower Miocene marks another phase of tectonic activity with extensive deposition of coarser clastic sediments in the central and southern blocks.
Cambay Basin | NDR – National Data Repository India
The total volume of seismic reflection data acquired from the Cambay Basin is of the order of LKM 2D and sq. The Early Tertiary sediments ranging in age from Paleocene to Early Eocene represent syn-rift stage of deposition that was controlled by faults and basement highs in an expanding rift system. Besides this, localized sandstone reservoirs within the Cambay Shale as in the Unawa, Linch, Mandhali, Mehsana, Sobhasan, fields, etc are also present.
This turned out to be a discovery well, which produced oil and gas.
Petroleum geology of the Cambay Basin, Gujarat., India in SearchWorks catalog
At places a gradational contact with the overlying Cambay Shale has also been noticed. Out of cakbay drilled, 97 are oil and gas bearing. In the following period, relative subsidence of the basin continued leading to the accumulation of the Younger Cambay Shale.
The lithological heterogeneity gave geeology to permeability barriers, which facilitated entrapment of hydrocarbons.
Seismic and drilled well data indicate a thickness of about 8 km of Tertiary sediments resting over the Deccan volcanics. Trap Rock The most significant factor that controlled the accumulation of hydrocarbons in the Olpad Formation is the favorable lithological change with structural support and short distance migration. There was a regional southward tilt of the entire rift basin during Late Eocene and it is marked by a regional marine transgression extending far to the north upto Sanchor basin.
The discovery of oil in Ankleshwar structure in gave boost to the exploration in the Cambay Basin.